This invention relates to material handling apparatus which employs an extendable arm in which an inner arm member can be slid relative to an outer encircling arm member to vary the effective length and thus the reach of the arm.
Such apparatus is well known. See, for example, U.S. Pat. No. 3,140,000 which discloses a backhoe digger with an extendable arm in the form of a dipper stick.
Although such apparatus functions adequately, it frequently presents a positional stability problem in that the inner arm is often, even when new, a relatively loose sliding fit in the outer member. Also even if the initial fit is good, a maintenance problem eventually arises since the wear between the sliding inner and outer arm members reaches a level which impedes the operation of the apparatus and this wear must be taken up by shims or wear plates which is a time consuming and often costly business.
It is an object of the present invention to provide an extendable material handling arm in which the sliding fit between the inner and outer members is relatively easily controlled, in which wear between the inner and outer slidable members is reduced and in which maintenance is also simplified.
Thus according to the present invention there is provide an extendable material handling arm comprising an outer member having a slot extending along the length thereof, an inner member provided with material handling means adjacent one end, the inner member being encircled by the outer member for sliding therein to vary the effective length of the arm, a first support structure carried by the inner member adjacent the end thereof remote from the material handling means, the first support structure including a support means having a support surface for sliding contact with longitudinally extending portions of the outer surface of the outer member adjacent the slot, and securing means extending through said slot for securing the support means to the inner member for sliding movement therewith so that said remote end of the inner member is supported within said outer member by holding said portions of the outer member adjacent the slot between said support means support surface and a support surface on the inner member and clearance is left between the inner and outer members along side portions opposite and remote from the slot.
If, for example, the outer member is of generally rectangular cross-section with the slot extending longitudinally down one side of the outer member the first support structure will pull the inner member into contact with the slotted side of the outer leaving clearance between the inner and outer members along their sides opposite the slot. This clearance will be present along substantially the entire length of the inner member within the outer member. Such an arrangement significantly simplifies manufacture since it removes the need for close control of the sliding fit between the inner and outer arm members. Also since contact between the inner and outer members is reduced wear is also reduced.
Preferably a second support structure is provided for sliding support of the inner member within the outer member at a location adjacent the end of the outer member nearest the material handling means so that direct contact between the inner and outer members is also avoided at this location.
Wear can be reduced still further by providing one or both support structures with low friction support surfaces made, for example, from self-lubricating cast nylon oil-impregnated material such as "Nylacast Oilon" sold by Nylacast Oilon Limited of Leicester, United Kingdom. If such an oil impregnated material is used, no lubrication of the sliding contact between the inner and outer members is necessary.
Preferably the first support structure supports the inner member against transverse movement within the outer member in directions at right angles to the direction of extent of the securing means. This transverse support is also preferably provided by surfaces of low friction material on the inner member for contact with the inner surface of the outer member.
The second support structure preferably comprises a collar on the outer member, the collar encircling the inner member and supporting detachable low friction wear pads which contact the outer surface of the inner member.
The areas of sliding contact between the support surface and the outer member are preferably disposed outwardly away from the slot to reduce any bending moment imposed on the outer member from the inner member via the first support structure.
The invention also provides a dipper stick for a backhoe in the form of an extendable arm as described above.